The invention relates to a bending apparatus for bending an elongated material that has various cross sectional shapes and is used for moldings of automobile window frames among other things.
Various kinds of bending apparatus have been proposed for bending elongated materials For example, U.S. Pat. No. 4,391,116 discloses a bending apparatus comprising a material feeding mechanism, a first guide roller element for positioning the material, a second guide roller element for bending the material and a slider mechanism for positioning the second guide roller element. The second guide roller element is connected to the slider mechanism with a universal joint mechanism and is able to incline freely The material feeding mechanism is arranged to hold the material between feeding rollers and support rollers, and feeds the materials by rotating the feeding rollers.
In bending, the material feed mechanism begins to feed the material, and the slider mechanism moves the second guide roller element to a predetermined position shifted against the first guide roller element. The material is bent in a continuous manner by feeding through both of the guide roller elements. In this case, the second guide roller element is tilted to be perpendicular to the feeding direction of the feed material. Because of this free tilting ability, the material is bent in desired curvature. In this conventional apparatus, however, after bending the material, the slider restores the second guide roller element to its original position while it is still inclined. This causes the material to be bent in an undesired direction. This also causes the material to be inserted badly, necessitating the positioning of the second guide roller element each time before starting to bend.
Moreover, the second guide roller element is supported by the universal joint mechanism vertically and horizontally. Thus when bending the material into a loop, the head of the bent material strikes the universal joint mechanism and is not able to bend any more.
In the material feeding mechanism, sometimes a slip occurs. A slip is caused between the material and the rollers due to bending resistance, so the material is not fed smoothly. Accordingly, the angle of inclination of the second guide roller element is unstable, and the material is not bent in the desired curvature.
In bending a hollow material, a mandrel is commonly used to prevent wrinkles, flattening of the material or thinning of the wall. The curvature of the material depends on the relative positions of the mandrel and the second guide roller element. Over time, the head of the mandrel is worn by friction, thus changing its relative position. The angle of inclination of the second guide roller element changes according to the wearing of the head of the mandrel, and precise bending is no longer executed.
Precise bending requires that the angle of the inclination of the second guide roller element be maintained precisely. In the conventional apparatus, however, the angle of inclination is determined by the universal joint mechanism, so precise bending is not executed.